I started writing this because all the 64 bit hash functions I came across were either too slow (FNV-1a, one byte at a time processing), or too large spanning hundreds of lines of code, or non-portable due to using hardware specific instructions. Being small and portable, the goal is to be able to use ChibiHash as a good "default" for non-cryptographic 64-bit hashing needs.
Some key features:
- Small: ~65 loc in C
- Fast: See benchmark table below
- Portable: Doesn't use hardware specific instructions (e.g SSE)
- Good Quality: Passes smhasher and smhasher3, so should be good quality (I think)
- Unencumbered: Released into the public domain
- Free of undefined behavior and gives same result regardless of host system's endianness.
- Non-cryptographic
Here's some benchmark (made via smhasher3) against other similar themed hash functions:
| Name | Large input (GiB/sec) | Small input (Cycles/Hash) |
|---|---|---|
| chibihash64 | 24.20 | 34 |
| xxhash64 | 15.10 | 50 |
| city64 | 18.30 | 47 |
| spooky64 | 16.68 | 70 |
| rapidhash.protected 1 | 21.50 | 32 |
| polymur-hash 1, 2 | 13.82 | 43 |
- Requires compiler/cpu support for retrieving the full 128 bit result of a 64x64 bit multiply.
- Universal, but has a complicated seeding step.
The introduction should make it clear on why you'd want to use this. Here are some reasons to avoid using this:
- For cryptographic purposes.
- For protecting against collision attacks (SipHash is the recommended one for this purpose).
- When you need very strong probability against collisions: ChibiHash does very minimal amount of mixing compared to other hashes (e.g xxhash64). And so chances of collision should in theory be higher.
A list of unofficial ports to other languages is maintained here.
- Faster performance on short string (42 cycles/hash vs 34 cycles/hash). The tail end handling has been reworked entirely with some inspiration from wyhash's short input reading.
- Better seeding. v1 seed only affected 64 bits of the initial state. v2 seed affects the full 256 bits. This allows it to pass smhasher3's SeedBlockLen and SeedBlockOffset tests.
- Slightly better mixing in bulk handling.
- Passes all 252 tests in smhasher3 (commit 34093a3), v1 failed 3.